NYGM 2.2 Escort Logic Question

[SubConscious]

I'm on my second patrol, it's November 13, 1939 and I'm in a VIIB off the southern coast of Ireland. I was sinking a tugboat with deck gun and 20mm fire when two destroyers came on the scene. Not a problem, I'm figuring the tugboat sent out a distress call.

So I crash dive deep, make a 90 degree turn, drop my speed to 1 knot and start trying to minimize my profile to the escorts. They manage to blow off one of my rudders, but I don't take any other serious damage, with hull efficiency at 99%.

A few game hours pass and I notice a third escort on the scene. Then a fourth. Then a fifth. I see on the navigation map that I'm near fairly deep water (200+ meters), so I creep for it, still trying in vain to evade.

Having reached the deep water, I wait for a depth charge attack. Once it arrives (didn't have to wait long with six escorts on me), I killed my engines and let my boat settle to the bottom, which was 211 meters. After several hours, a sixth escort arrived on the scene.

Ok, so that's the scenario. These six escorts have been on station for so long, well over 24 hours, that I'm at about 20% oxygen and they're showing no signs of giving up.

Here's my question: Is this realistic? I can't recall a single instance of a U-boat being hounded by six escorts for this long, especially in 1939. I can't see why a pair of destroyers would need to call for reinforcements unless they ran out of depth charges. Once my boat when to the bottom, I could see leaving 1-2 escorts on station to wait and listen, but all six?

Any clarification would be greatly appreciated. Thanks!